This invention relates generally to lasers, and more particularly to high efficiency, high power blue-green lasers useful for underwater communication and detection systems.
Blue-green lasers are very desirable for underwater uses due to their low transmission losses in water. Existing blue-green lasers for such underwater uses are the frequency doubled Nd doped YAG laser, Cu vapor lasers and various dye lasers. A problem common to these existing lasers is low efficiency (generally less than 1%) thus necessitating very high iuput power levels to obtain output pulses sufficiently powerful for communication and detection systems. Typically a pulse of about 20 nsec duration containing 1 Joule of energy per pulse at a rate of 100 to 1000 pps is desired. The high input power requirements necessary to attain such output pulses brings about the need for large power sources which can be very impractical in carrier vehicles such as aircraft or submarines where space and weight considerations are critical.
Recently it has been found that a relatively efficient blue-green laser can be made by pumping a dye laser such a 4-MU (coumarin) with a mercury capillarly lamp. In articles by Dal Pozzo et al entitled "Pulsed Mercury Capillary Lamps for Dye Lasers Pumping: Spectral Measurements" and "Pulsed High-Pressure Mercury Capillary Lamps: A New Way of Pumping Dye Lasers", published in Applied Physics, Vol. 6 (1975) pp. 341-344 and 381-382 respectively, and incorporated herein by reference, spectral matches between the mercury capillary lamp and the 4-MU pump band were found to be as high as 24% giving an output in the blue with a pulse duration of 40 .mu.sec. This would lead to an expected overall laser efficiency of over 5%. However, the long pulse duration and low peak power output of this laser is not sufficient for most desired communication and detection uses.